It involves the concept of purinergic signaling, in which an increased distal tubular sodium chloride concentration causes a basolateral release of adenosine from the macula densa cells.
[1][2][3] The kidney maintains the electrolyte concentrations, osmolality, and acid-base balance of blood plasma within the narrow limits that are compatible with effective cellular function; and the kidney participates in blood pressure regulation and in the maintenance of steady whole-organism water volume [4] Fluid flow through the nephron must be kept within a narrow range for normal renal function in order to not compromise the ability of the nephron to maintain salt and water balance.
Active transepithelial transport is used by the thick ascending limb of loop of Henle (TAL) cells to pump NaCl to the surrounding interstitium from luminal fluid.
[6] The TGF mechanism is a negative feedback loop in which the chloride ion concentration is sensed downstream in the nephron by the macula densa (MD) cells in the tubular wall near the end of TAL and the glomerulus.
[5] Vasodilation of the afferent arteriole, which results in increased glomerular filtration pressure and tubular fluid flow, occurs when MD cells detect a chloride concentration that is below a target value.
The macula densa is a collection of densely packed epithelial cells at the junction of the thick ascending limb (TAL) and distal convoluted tubule (DCT).
The macula densa's detection of elevated sodium chloride concentration in the tubular lumen, which leads to a decrease in GFR, is based on the concept of purinergic signaling.
A high protein diet affects the feedback activity by making the single nephron glomerular filtration rate higher, and the Na and Cl concentrations in early distal tubule fluid lower.